1. Field of the Invention
This invention relates to the field of hydrocarbon production processes and more specifically to removal of hydrogen sulfide in downhole oil and gas field applications.
2. Background of the Invention
During the drilling, production, and transportation of crude oil, hazardous hydrogen sulfide may often be encountered in many hydrocarbon containing fluids. For instance, when crude oil is extracted, it is typically in contact with water and gas. During downstream separation of the oil and water, hydrogen sulfide may be released as a gas from the associated oil and water phases. Hydrogen sulfide may pose health hazards as well as corrosion issues and potential reactions with other hydrocarbons.
Numerous approaches to these problems have been developed. Such developments to control hydrogen sulfide downhole include solid scavengers (i.e., such as zinc oxide or other metal oxides) for complexing hydrogen sulfide in solid form, liquid scavengers (i.e., such as amines, morpholine, or acrolein) for complexing hydrogen sulfide in liquid form, and oxidizing chemicals (i.e., mild oxidizers such as nitrite or long-chain amine oxides and strong oxidizers such as peroxides) that convert hydrogen sulfide to more harmless forms of sulfur such as elemental sulfur or thiosulfate.
There are drawbacks to these developments. For instance, metal oxide solid scavengers generally react reversibly with hydrogen sulfide. As a result, there is a risk of regeneration of hydrogen sulfide if pH changes are experienced during subsequent handling of the reaction product. Liquid scavengers may be cost effective and tie up hydrogen sulfide as water soluble compounds that may be discharged to wastewater treatment facilities. Some of these scavengers (i.e., acrolein) may tie up hydrogen sulfide in an irreversible manner. Other liquid scavengers (i.e., some amines) react with hydrogen sulfide reversibly, so there is potential for the re-evolution of hydrogen sulfide in subsequent handling. Oxidizing chemicals may irreversibly convert hydrogen sulfide to hamiless water soluble forms of sulfur that are compatible with effluent discharge. However, there are several potential complications with these chemicals. Long chain amine oxides may produce foaming due to their surfactancy and may involve large treatment volumes and/or cost in oilfield applications. These amine oxides also typically have limited efficiency for large amounts of hydrogen sulfide since they are normally diluted in water to prevent gel formation. Oxidation using nitrites may produce ammonia as a by-product that may, in turn, potentially stall the sulfide oxidation before it is complete. The nitrite oxidation reaction may also be accompanied by a rise in pH, which may cease the oxidation before it is complete. Stronger oxidizers, such as permanganate or peroxides, may be quite non-selective in their reaction and may be reactive with many of the hydrocarbon components that exist downhole. For instance, strong oxidizers may react with hydrocarbon components in crude oil and may also generate harmful reaction products such as chlorine in the case of hypochlorite. Permanganate may produce solid manganese dioxide as a reaction product, which may be inefficient for oilfield operations and may be especially prohibitive in downhole applications where the reaction product may pose plugging issues. Peroxide is typically very temperature sensitive and may decompose rapidly at elevated temperatures and a pH above 7, which are very typical in oilfield applications.
Consequently, there is a need for an improved method for removing hydrogen sulfide from hydrocarbon containing fluids.